The present invention relates to a wireless communication system. More specifically, the present invention relates to an anti-interference method and device for a wireless communication system.
A wireless communication system consists of three parts (i.e., a transmitting apparatus, receiving apparatus, and radio channel) and utilizes radio waves to communicate information and data. Wireless communication is widely used because of the great convenience of the communication thereof. Cellular networking became a main networking method for wireless communication because of good coverage, reasonable networking cost, and high utility efficiency of frequency spectrum resources thereof. In the cellular networking, a base station is the center of a cell and needs to communicate with all the terminals in the cell. Since the distance between the base station and each terminal is different, the modulation mode of each terminal is different, and the strength of the signal received in the base station is different, the base station should have a wide receiving dynamic range. In order to ensure that signals from different terminals can be received correctly, a conventional base station mainly works in the following way:                1. An Analogue to Digital Converter (ADC) with a wide bit-width is used. Generally speaking, an ADC with 12 bits or more is a good choice. However, since the cost of a high rate ADC with 12 bits or more is high, an ADC with 11 bits is widely used in practice.        2. The Automatic Gain Control (AGC) is used to adjust the gain of a receiver of the base station. The AGC technology is one of the most important technologies for a communication receiving apparatus. Because of the limitation of the number of bits of the ADC, it is not possible to provide a very wide receiving dynamic range merely by means of the ADC. Therefore, in order to further increase the dynamic range of the receiver, the AGC technology is generally needed at the receiver side. The main function of the AGC is to maintain the level of the signal output from a front end radio frequency amplifying circuit at a certain value when the signal arrives at the ADC. The AGC can automatically ensure that the front end variable gain amplifier is in a high gain position upon reception of a weak signal, while the front end variable gain amplifier is in a low gain position upon reception of a strong signal, so that the output signal is maintained at a proper level. Therefore, the following cases can be avoided: where the input signal is too small to ensure the accuracy of the output of the ADC or where the input signal is too large, which saturates the ADC to distort the signal.        3. The Power Control technology is used. The transmitting power of each terminal is adjusted so that the strength of a signal that arrives at the base station from each terminal is in a relatively close range. Thereby, it is possible to reduce the requirement on the dynamic range of the base station. On the premise that the communication quality is ensured, the power control will make the transmitting power as small as possible. Therefore, the power control technology can save the power consumption of a terminal. Meanwhile, it is also possible to reduce the mutual interference between terminals.        
The effects of these technologies applied to a conventional base station are very good because there is no interference from other wireless systems. However, since radio spectra become rare, it becomes increasingly urgent to share radio spectrum resources. When radio spectrum resources are shared, interference from a heterogeneous system is inevitable. In the Industrial Scientific Medical (ISM) frequency bands, which are mainly used for industrial, scientific, and medical organizations, no license is needed and it is only necessary to comply with a certain transmitting power (generally lower than 1 W) and not to interfere with other frequency bands. In the ISM frequency bands, the 2.4 GHz frequency band is an ISM frequency band commonly used by many countries. Many different wireless communication systems coexist (e.g., WIFI, Bluetooth, Zigbee, etc). These communication systems cannot work at the same time because they occupy wide bandwidths and cause strong interference with each other. They can share frequency spectra only by using a back-off method. For a new broadband system, all in-band signals from heterogeneous systems are considered interference signals. Most narrow band signals have a very strong power spectrum density, while broadband signals have low power spectrum density and are susceptible to interference from narrow band signals and thus cannot work normally. Therefore, the coexistence of broadband signals and narrow band signals becomes a big challenge.
The conventional gain control technology does not consider the factor of heterogeneous interference. In the case of strong burst interference, the ADC can be saturated easily and introduce a large error, so that uplink signals cannot be decoded. Additionally, since real signal power can not be estimated correctly in the case of the saturated ADC, the adjustment step of the gain control is not accurate. As a result, it takes a long time to achieve an accurate adjustment. However, since the interference comes suddenly, there is often a difficult situation: when the AGC catches up with the change in the signal, the interference disappears. At this point, the AGC can return to be in the range of a normal signal after some adjustment steps. These adjustments are often accompanied by a large number of error codes. If the AGC is simply set to correspond to the strongest interference, the overall noise coefficient of the system will increase significantly so that the terminal has to transmit higher uplink transmitting power for normal communication. As a result, the coverage of the whole system is reduced significantly.
For a new broadband system, all in-band signals from heterogeneous systems are considered interference signals. Most narrow band signals have very strong power spectrum density, while broadband signals have low power spectrum density and are susceptible to interference from narrow band signals and thus cannot work normally. The conventional power control technology does not consider the factor of heterogeneous interference and thus is not applicable any longer.
Therefore, it is desirable to provide an anti-interference method of a wireless communication system, which is able to ensure the communication quality of the wireless communication system in the case that there is strong burst interference.